Various types of polyethylenes are known in the art and, high density, low density, and linear low density polyethylenes are some of the most useful. Low density polyethylene is generally prepared at high pressure using free radical initiators, or in gas phase processes using Ziegler-Natta or vanadium catalysts, and typically has a density in the range of 0.916 to 0.950 g/cm3. Typical low density polyethylene produced using free radical initiators is known in the industry as “LDPE”. LDPE is also known as “branched” or “heterogeneously branched” polyethylene because of the relatively large number of long chain branches extending from the main polymer backbone. Polyethylene in the same density range, i.e., 0.916 to 0.940 g/cm3, which is linear and does not contain long chain branching, is known as “linear low density polyethylene” (“LLDPE”) and is typically produced with conventional Ziegler-Natta catalysts or with metallocene catalysts. Polyethylenes having still greater density are the high density polyethylenes (“HDPEs”), i.e., polyethylenes having densities greater than 0.940 g/cm3, and are generally prepared with Ziegler-Natta catalysts. Very low density polyethylenes (“VLDPEs”) are also known. VLDPEs can be produced by a number of different processes yielding polyethylenes having a density less than 0.916 g/cm3, typically 0.890 to 0.915 g/cm3 or 0.900 to 0.915 g/cm3.
A majority of global LDPE and LLDPE demand includes film, carrying bag, and sack applications. Some examples of these applications include agricultural, multi-layer, and shrink films. LDPE, which is soft, ductile, and flexible, is additionally utilized for strong, elastic goods, such as screw caps, lids, and coatings. There remains a demand for LDPE and LLDPE in the global marketplace, and consequently there is a continued need for improvements that provide cost savings.
Some improvements include using a different catalyst system. For example, some work has been done to provide branched polymers having a density of 0.940 g/cm3 or less using metallocene compounds. JP2011-089019A discloses a bridged metallocene in combination with a cocatalyst (a modified clay mineral, an alkyl alumoxane or an ionized ionic compound) and an organoaluminum compound for olefin polymerization which can produce a polyolefin which possesses long chain branching with high activity.
Pyridyl amines have been used to prepare Group 4 complexes which are useful transition metal components for use in the polymerization of alkenes, see for example US 2002/0142912; U.S. Pat. No. 6,900,321; and U.S. Pat. No. 6,103,657, where the ligands have been used in complexes in which the ligands are coordinated in a bidentate fashion to the transition metal atom.
Other improvements have focused on the support technology. Alternative supports for metallocene and single-site catalysts have been the subject of numerous ongoing research projects. In particular, metallocenes supported on clay or ion-exchanged layered compounds have generated a great deal of interest. Olefin polymerization catalysts using clay, clay mineral, or acid/salt-treated (or a combination of both) ion-exchange layered compounds, an organoaluminum compound and a metallocene as components have been reported (see EP 0,511,665A2; EP 0,511,665B1; and U.S. Pat. No. 5,308,811). Likewise, U.S. Pat. No. 5,928,982 and U.S. Pat. No. 5,973,084 report olefin polymerization catalysts containing an acid or salt-treated (or a combination of both) ion exchange layered silicate, containing less than 1% by weight water, an organoaluminum compound and a metallocene. Furthermore, WO 01/42320 A1 discloses combinations of clay or clay derivatives as a catalyst support, an activator comprising any Group 1-12 metal or Group 13 metalloid, other than organoaluminum compound, and a Group 3-13 metal complex. Also, U.S. Pat. No. 6,531,552B2 and EP 1,160,261 A1 report an olefin polymerization catalyst of an ion-exchange layered compound having particular acid strength and acid site densities. US 2003/0027950 A1 reports an olefin polymerization catalyst utilizing ion-exchange layered silicates with a specific pore size distribution and having a carrier strength within a specific range.
U.S. Pat. No. 7,220,695 discloses catalyst systems comprising, inter alia, metallocene catalysts and supported activator systems comprising an ion-exchange layered silicate, an organoaluminum compound, and a heterocyclic organic compound, see Example 7 et seq.
U.S. Pat. No. 6,559,090 discloses a coordinating catalyst system comprising at least one metallocene or constrained geometry pre-catalyst transition metal compound, (e.g., di-(n-butylcyclopentadienyl)zirconium dichloride), at least one support-activator (e.g., spray dried silica/clay agglomerate), and, optionally, at least one organometallic compound (e.g., triisobutyl aluminum), in controlled amounts, and methods for preparing the same.
Accordingly, there is a need for new processes to produce low cost LLDPE or HDPE over a wide molecular weight range. More specifically, there is a need for new supported catalyst systems, particularly supported pyridyldiamido catalyst systems, to produce new polyethylenes, such as high molecular weight polyethylenes, which can be useful as a component in bimodal high density PE resins for pipe applications, film, or blow molding, particularly such with layered silicates dispersed therein. It is further desirable that these new pyridyldiamido catalyst systems are robust and have high productivity, particularly in gas phase polymerization processes, and can even be used as a single component supported catalyst or in a mixed component catalyst system.